With few exceptions, the genetic codes of all known organisms specify the same 20 canonical amino acid building blocks which sufficiently encode three dimensional protein structures. However, many proteins also require additional chemical groups beyond what the 20 building blocks can provide to carry out their native functions. Accordingly, approaches to synthesize proteins with defined posttranslational modifications have been developed for both research and therapeutic purposes. One such method is to genetically incorporate non-canonical amino acids (NAAs) directly into proteins during translation in live cells. However, such methods are limited in terms of efficiency, especially when multiple NAAs must be genetically incorporated into a protein. Accordingly, there is currently a need to develop more efficient methods, cells and systems for genetically incorporating non-canonical amino acids into proteins.